This invention relates to a door closer control and assist linkage, and more particularly, to a control linkage for use with a door closer, in which a resilient element serves to augment and assist door control forces produced by the door closer to aid in the operation of the closer.
Hydraulic door closers such as those illustrated in U.S. Pat. No. 3,082,471 to Rolph, issued Mar. 26, 1963, U.S. Pat. No. 3,259,936, to Sheridan, issued July 12, 1966, and U.S. Pat. No. 4,019,220 to Lieberman, issued Apr. 26, 1977 and assigned to the assignee of this application, are of the general type to which this invention relates. Such door closers utilize a spring-urged hydraulic piston to bias a door to its closed position, and also provide a hydraulic back-check to smoothly retard and cushion movement of the door as it approaches its extreme open position. Typically, the force generated by the door closer unit is transmitted between the unit and fixed structure such as the door frame through a linkage, generally consisting of the pair of links, pivotably coupled to the unit and to a soffit plate mounted on the door frame.
Because the internal mechanism of closer units is hydraulic, the ability of a unit to cushion back-check forces is determined by, among other factors, the configuration of its hydraulic system, the spring and hydraulic characteristics of which control the return movement of the piston, and the geometry of the linkage by which forces are transmitted between the output of the closer and the door.
A shortcoming of existing door closer apparatus is the fact that, due to both the internal structure of the closer and control arm geometry, the opening and closing forces perceived at the door are at a relatively low level when the door is at or approaching its door-open limit position.
This characteristic can be a serious drawback in certain applications, such as in exterior doors subject to heavy traffic or drafts. Many commercially available door closers units do not, in such applications, provide either a closing force adequate to overcome the retarding effect of drafts or an effective back-check.